2. The answer to whether it's OK to leave it on is complex. I posted something about this in another thread some days ago, but I can't recall the thread at the moment.

The short answer is yes, every component is designed to be able to stand a continuous power-up state. And it may be argued that those compnents are under more stress at the moment they are being powered up. This is why some people claim that it's better to NEVER turn off your computer.

However, those same components undergo less but more extended stress while on. Moving parts like HDDs and fans are subjected to mechanical wear and tear, while purely electrical components are under thermal stress.

My personal opinion is that it's OK to leave it on as long as you need it to do something, but turn it off if it's going to be idle for an extended period.

3. Technically yes, reducing clock speed will reduce CPU power drain, and also produce less heat and extend the life of your CPU. But the saving in terms of electricity bill or UPS battery drain will be very small.

4. These stand for 0.7 Volts and 1.0 Volts. They are two different standard values of the strength (in terms of voltage) of the picture information your graphics card sends to your monitor.